1. Field of the Invention
The invention relates to an apparatus for depositing polycrystalline diamond by plasma technology onto flat substrates of large area, having a vacuum chamber, an airlock for the entry and exit of the substrates, and with a system within the vacuum chamber for passing the substrates through the vacuum chamber.
2. Description of the Related Art
A known apparatus for the production of plasma (DE 195 03 205) makes it possible to produce plasmas for surface treatments and coating processes in a limited range of operation (process area, gas pressure, microwave power). The known apparatus consists substantially of a cylindrical glass tube installed in a vacuum process chamber and a metallically conductive tube situated in the latter, and atmospheric pressure prevails in the interior of the glass tube. Microwave power is introduced through the walls of the vacuum process chamber bilaterally through two inputs and two metal coaxial conductors consisting of an inner conductor and an outer conductor. The outside conductor of the coaxial conductor inside of the vacuum process chamber is replaced by a plasma discharge which if the ignition conditions are sufficient, a plasma gas is ignited and sustained by the microwave power, while the microwave power can issue from the two metallic coaxial conductors and pass through the glass tube into the vacuum processing chamber. The plasma externally envelops the cylindrical gas tube and together with the inside conductor forms a coaxial conductor with a very high attenuation coefficient. With a fixed microwave power delivered on both sides, the gas pressure in the vacuum process chamber can be adjusted such that the plasma apparently burns uniformly along the apparatus where the outside conductor of the coaxial line inside of the vacuum process chamber is missing.
An apparatus for producing a plasma in a vacuum chamber has already been proposed (Patent Application DE 197 22 272.2), in which a rod-shaped conductor is carried through the vacuum chamber within a tube of insulating material, and the inside diameter of the insulating tube is greater than the diameter of the conductor, the insulating tube is held at both ends in walls of the vacuum chamber and is sealed to the walls at its external surface, and the conductor is connected at both ends to a first source for producing the alternating electromagnetic fields, and is surrounded in the area of both points of passage through the walls and for at least a short distance towards its central portion by tubular pieces of electrically conductive material, the two tubular pieces being disposed concentrically with the insulating tube, and the cylindrical spaces formed by the insulating tube and the tubular pieces are connected to a second source for the production of an alternating electromagnetic field.
It has long been known to grow diamond on diamond substrates (Vakuumbeschichtung 5, Anwendungen Teil II, Prof. Dr. G. Kienel, VDI-Verlag GmbH, Duesseldorf 1993).
Furthermore, the importance of atomic hydrogen during the growing process has been found. It is furthermore also known to deposit diamond coatings by hot filament methods by all kinds of plasma CVD (microwaves, RF, DC, arc discharges, plasma jet) and from C2H2/O2 flames.
Furthermore, methods utilizing hot-wire sources, especially the parameters necessary therefor, such as pressures and process gas compositions, have been extensively described in xe2x80x9cProperties and Growth of Diamond,xe2x80x9d by Gordon Davies, Kings College, London UK, published by INSPEC, the Institution of Electrical Engineers, 1994, and in xe2x80x9cCurrent and Prospective Fields of Application for Diamond thin Films,xe2x80x9d by Michael Liehr, April 1995, Department of Physics, Heriot-Watt University, Edinburgh.
Lastly, an apparatus for depositing polycrystalline diamond on flat substrates of large area has been proposed (Patent Application DE 196 31 407), consisting of a vacuum chamber with locks for the entry and exit of the substrates, with a system disposed in the chamber for carrying the substrates through at least one, but preferably two, treatment stations, and with hot wire sources provided above the substrate plane and forming a first group, and with microwave plasma sources forming a second group, and with an electrode underneath the substrate plane and fed with radio frequency for producing a bias voltage, and with gas feeding tubes leading into the vacuum chamber, the hot wire systems being configured as line sources and extending across the direction of substrate transport and forming a first coating zone, the microwave plasma sources being arranged in a row spaced from and parallel to the hot wire sources, and together forming a second coating zone.
The present invention is addressed to the problem of coating large, planar substrate surfaces with super-hard carbon coatings of uniform thickness and quality.
This problem is solved according to the invention by a plurality of linear microwave plasma sources arranged parallel to one another and in a common plane above the substrates and extending transversely across the direction of substrate movement, with gas inlet and gas outlet tubes opening into the process chamber, a plurality of gas inlet and gas outlet tubes distributed over the length of the linear source being associated with each of the linear sources, and the outlet openings of the gas inlet tubes being situated immediately above the linear source, and the openings of the gas outlet tubes being arranged each in the area between two linear sources and in a plane which extends approximately through the core axes of the linear sources.
Additional details and features are described and characterized in the claims.